1. Field of the Invention
The present invention relates to a single device having independently controlled circuits and, more particularly, a pump having first and second independently controlled circuits. It finds particular application as a control system for a variable displacement pump used in an engine geometry control system and, more particularly, to an improved control system for a variable exhaust nozzle on a gas turbine engine and will be described with particular reference thereto. However, it will be appreciated that the present invention is also amenable to other like applications.
2. Discussion of the Art
Engine geometry control systems are in widespread use on modern aircraft turbine engines. Engine geometry controls are used for various actuation of IGV, VSV, VBV, VEN, and other subsystem actuators. Additionally, engine geometry control systems are often required to provide engine start flow.
Engine geometry control systems are generally required to have the capability to control high pressure to either a rod end or piston end of an actuation system. This usually requires the high pressure side of a fluid source to be switched from the rod end to the head end of an actuator, or vice versa.
Switching from one end to the other is generally accomplished by using appropriate control valves to switch the high and low pressure of the fluid supply as demanded by the engine geometry requirements. Depending on the number of actuators to be handled in a given system, the flow change may be accomplished by valves in the supply system or by valves in the actuator. The valves serve to switch the inlet and discharge flow sources.
Generally, the fluid flow source or pumping system must be a variable displacement pump to minimize input power and heat loss due to the high pressures required. The control system response must be fast enough to enable changes from minimum flow to full stroke flow in a very short period. Minimum flow condition is often only needed to supply leakage makeup or cooling flow, whereas full stroke flow is often needed during takeoff or times of maximum actuator movement. The time limitation for the change to occur is dependent on the system needs and the number of actuators being serviced.
Heretofore, high pressure pumps have generally been limited to piston pumps of various configurations. However, these pumps often require extra complexity and expense in order to meet the high pressure and low lubricity fuel requirements of aircraft engine jet fuels. Further, these pumps have not had a history of high reliability.
In any case, the pumping system may be self pressure compensated or externally servo controlled. A pressure compensated pumping system is capable of maintaining a fixed discharge pressure while supplying only the flow needed by the load system. A servo controlled variable displacement pump can vary both the flow and pressure in response to the load system needs.
A variation of a servo control method is to use an over-center servo pump. An over-center servo pump is capable of switching its inlet and discharge porting in response to system demands. A major drawback of the over-center servo pump is that it is normally limited to a piston type pump design and is often unduly complex when discharge pressure requirements reach the 3000-5000 psid range.
Another major drawback of prior art systems is that the components of the system are often numerous, voluminous, heavy and have experienced maintenance problems.
Accordingly, there is a need for an engine geometry control system that does not suffer the disadvantages of the prior art and overcomes the above-referenced drawbacks.
The present invention relates to a system that provides two independently controllable circuits from a single device. An exemplary embodiment of the present invention relates to an improved control system for a variable exhaust nozzle on a gas turbine engine.
In accordance with the present invention, a housing includes a rotor and a split cam ring that defines first and second independent pump circuits. Each circuit is independently controllable.
One advantage of the present invention is the provision of an improved control system for a variable exhaust nozzle on a gas turbine engine which provides a simplified system integration.
Another advantage of the present invention is the provision of an improved control system that enhances performance and stability.
Yet another advantage of the present invention is the provision of an improved control system that enhances service life and reliability.
Still another advantage of the present invention is the provision of an improved control system that is less heavy, less voluminous and less costly than prior art systems.
A still further advantage of the present invention is the provision of an improved control system that reduces system complexity with improved stability.
Another advantage of the present invention is the provision of an improved control system that reduces system temperature.
Further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.